1. Field of the Invention
The present invention relates to an apparatus for detecting the rotational angle of a crank (crank angle) of a crankshaft of an internal combustion engine. More specifically, the present invention pertains to an apparatus and method suitable for detecting the crank angle of a specific cylinder in a multi-cylinder internal combustion engine.
2. Description of the Related Art
Various timing controls related to the piston stroke of the engine, such as ignition timing control and fuel injection timing control, are executed in accordance with the crank angle of the engine, which is detected by a crank angle detection apparatus.
In an engine where the drive force is obtained from the reciprocating movement of a piston, it has been a custom to convert the reciprocating motion into the rotating motion by connecting the piston to a crank (or crank pin) of a crankshaft via a connecting rod. Therefore, the piston position in the cylinder is determined by the crank rotating angle (hereinafter referred to as crank angle). Each stroke (or piston position) in the cylinder from the intake stroke to the discharge stroke based on the piston position can be identified by detecting the crank angle.
Japanese Unexamined Patent Publication No. 5-288112 describes an apparatus provided with an engine speed sensor arranged in the vicinity of the crankshaft and a sensor arranged in the vicinity of a camshaft to identify a particular cylinder. A timing rotor, which is a part of the engine rotating sensor, has a plurality of equally spaced teeth. However, a tooth is missing at one location, which produces a gap.
In this apparatus, the engine speed sensor issues a signal each time the gap passes by an electromagnetic pickup. The signal is used as a reference position signal. A controller counts the number of pulses received from the speed sensor after the reference position signal output is received. When the number of counts counted by the counter reaches a predetermined value, the controller calculates the crank angle of a particular cylinder based on the signal from a cylinder identifying sensor.
Since the crankshaft makes two rotations (720° CA) per cycle, it can not be determined whether the crank angle lies between 0° CA and 360° CA or between 360° CA and 720° CA (0° CA and 360° CA during the second rotation) if the judgment is done only based on the signals from the crankshaft (or crank). Therefore, in order to identify a particular cylinder, an identifying signal issued in correspondence with the camshaft, which makes one rotation (720° CA) per cycle, is used to determine whether the crank angle lies between 0° CA and 360° CA or between 360° CA and 720° CA (0° CA and 360° CA of the second rotation).
Thus, it is possible to determine the crank angle for any cylinder of a multi-cylinder engine and specify a cylinder to be ignited or fuel-injected with the help of the engine speed sensor and the cylinder identifying sensor. Moreover, since the cylinder identification signal is issued close to the time that the reference position signal is output, it is possible to determine the cylinder from the beginning of cranking to the reference position signal even if the crank angle is not memorized when the engine is stopped.
However, in the above-mentioned apparatus, the engine speed sensor is arranged in the vicinity of the crankshaft and the cylinder identifying sensor is arranged in the vicinity of the camshaft. Thus, it is necessary to provide two independent sensors to detect the crank angle. This adds complexity to the maintenance of the system.
The above problem may be solved by providing one sensor in the vicinity of the camshaft that functions as both the engine speed sensor and as the cylinder identifying sensor. However, since the camshaft is driven by the crankshaft by means of a timing chain, a timing belt, or other parts, it is impossible to detect timing accurately with such a method due to vibrations of the timing belt or other factors.
In addition, since various data for detecting the crank angle are not memorized when the engine is stopped, cranking is required until the cylinder identifying signal is issued when restarting the engine.